Simply go beyond sell price where more than 1 supplier is available.
Create Excel sheet where e.g. point are automatically calculated against criteria, based on:
a) objective metrics as:
- quality performance (quality discipline)
- delivery performance (logistic/purchasing discipline)
b) subjective metrics as:
- smoothness of new product implementation (purchasing/technical discipline)
- openness of claim support (quality discipline)
c) other worth (or) less aspects, as
- standard against which supplier's quality management system is certified (purchasing/quality discipline)
- second party audit results (purchasing/quality discipline)
- payment terms (accounting discipline)
etcetera, etcetera and you have more than 1 discipline, we can even say you have multi-discipline.
Excel will tell you - take this one or another.
Without sheet nonconformity shall be raised.